fields such as electronics, medical engineering and aerospace, femtosecond
(fs = 1 x 10-15s) laser pulses could offer considerable advantages over
conventional nanosecond lasers for high precision micro-machining of problematic
and delicate materials. BRITE/EURAM project FEMTO, co-ordinated by Laser
Zentrum Hannover (LZH), brings together researchers, equipment manufacturers
and end users in a combined effort to design and test an easy-to-use system
suitable for industrial application.
laser machining enables a wide variety of materials - from metals,
ceramics and glass, to heat-sensitive plastics - to be shaped with
very high precision. The ultra-short duration of the high-energy
pulses enables relatively high material removal rates to be achieved,
with minimal thermal and mechanical damage. Processing is thus not
only precise, but also more repeatable. To date, however, its use
has been limited by the fact that the available equipment is bulky
therefore sought to use its extensive experience of the technology
in a research environment as a basis for developing a routine tool
that would be of value to various sectors of European industry.
search for collaborators produced a consortium bringing together
a wide range of relevant expertise. The partners include Thompson
CSF-Laser, who at the start of the project were Europe's only supplier
of femtosecond solid-state lasers (based on titanium-sapphire),
and laser machine manufacturer Exitech.
The University of Bordeaux's Equipe Laser Intense et Applications
(ELIA) contributes further research capability, while medical implant
a producer of specialised camera tubes and detectors, are both potential
industrial users of the resultant technology.
group was able to attract the necessary funding, and the three-year
project was launched in September 1998. This concentrated initially
on studying the interaction of lasers with different types of material,
using the available research-scale equipment. Promising applications
were targeted in the domains of each of the two end-user partners.
Photek, the aim was to replace electro forming and Electro Discharge
Machining (EDM) by laser ablation for the production of components
such as the metal accelerator grids employed in photomultiplier
tubes and other devices. By enabling the perforations to be reduced
down to the micron scale, this would open the door to new applications,
including detectors for ultra-fast electronic signal measuring instruments
and fluorescence microscopy imaging.
far, the machining of metals has proved to be rather slow and problematic
- but LZH recently supplied a batch of apparently successful samples
for evaluation by Photek. Trials will shortly commence.
greater progress has been made in the medical field - where Biotronik
sought, in particular, to explore the manufacture of biodegradable
stents for use in minimal invasive heart surgery. A stent is a slotted
tube that is inserted into a blocked blood vessel after dilation,
in order to prevent subsequent closure. To date, these have typically
been manufactured in stainless steel or nickel-based shape-memory
alloys. Quite often such support is required only for a period of
some months, but the metal stent cannot be removed from the vessel
at a later date. In some 20-30% of cases, however, its invasive
nature actually provokes reblockage.
FEMTO team has therefore been studying the use of biodegradable
polymers. While work goes on to optimise the actual design, femtosecond
laser technology has already proved to be a practical means of fabricating
the stents. Around 100 of these have been produced to date. They
are currently undergoing testing, both to assess the effect of the
laser treatment on the material properties and to evaluate performance
in terms of mechanical stability, degradation time and solubility.
Some in situ experiments have been conducted with animals, but human
trials remain some way off.
the same time, the production of a prototype industrial machine
is nearing completion. By developing a purpose-designed laser generator
with significantly fewer parameter variation options than are necessary
in a research system, Thompson CSF-Laser succeeded in reducing the
dimensions down to an acceptable size. Working in parallel, Exitech
has built an initial micro-machining station dedicated to manufacture
of stents as well as grids. The two elements will be assembled and
tested before the year-end. The complete unit will delivered to
LZH early in 2001 to permit further optimisation and more extended
trials. A finalised version is likely to be adopted for commercial
production by the partners in eighteen months to two years.
the initial problems in machining metals, Exitech considers that
the technology also shows real promise for applications such as
the manufacture of micromoulds and fuel injector nozzles, as well
as burr-free drilling of printed circuit boards. LZH will also continue
to experiment with other polymers. The consortium considers that
its progress to date puts it significantly ahead of US rivals.
targeting machine tools production under the Innovative
products, processes and organisation key action goes beyond
improvements in traditional machine tool-making. Rapid and high-precision
laser technology is leading to the development of delicate materials
for use in a variety of disciplines, including medical instruments
- Precise machining by femtosecond laser pulses (BRPR980694)